Although inserting another stent into the narrowed artery will solve the problem in a short time, some of the vessels will again narrow, explains Yoshihiro Morino, M.D., a research fellow at Stanford University Medical Center, Stanford, Calif.
“The question of whether to re-stent or not to re-stent is an ongoing debate, so our study was designed to address this issue,” he says.
Led by Peter Fitzgerald, M.D., Ph.D., director of the Cardiovascular Core Analysis Laboratory at Stanford, Morino and his colleagues analyzed 70 cases of in-stent restenosis. Of these, 34 patients received radiation in their re-narrowed arteries, while 36 made up the placebo group and had no radiation. The 34 patients who had irradiated lesions were divided into four groups: old stent not re-stented; old/new stent overlap, new stent only and lesions treated without re-stenting.
The researchers analyzed the success of the procedure with volumetric intravascular ultrasound, an imaging technique that allows them to measure the interior dimensions of the artery. The ultrasound examinations were done at the time patients where treated for in-stent restenosis and again six months later. The measurement is called lumen volume index (LVI). Higher LVI means blood flows more easily through the vessel.
In patients treated with radiation, the lumen volume was larger for the re-stented segments than the non-stented. However, at follow-up, researchers found that the lumen volume was similar for the re-stented and the non-restented segments, due to the increase in new cells growth around the lesion, which is called neointimal hyperplasia.
LVI was about 7 for stented lesions versus about 6 for non-stented lesions after intervention. However, at follow-up the LVI was reduced to about 6 – equal to that of the lesions that were not re-stented.
Placebo patients had a similar outcome: placing new stents or overlapping a new stent with the original stent initially demonstrated good results, but that benefit too disappeared after six months.
New cell growth was almost twice as common in re-stented segments treated with irradiation compared to those restented segments not treated with radiation.
“Based on this analysis, bare stents do not achieve a good long term outcome. And regardless of supplementary radiation, repeat stenting strategies provided little long-term advantage. Radiation is best reserved for those lesions that are not restented.
Morino theorized that the same problem that causes initial stent failure causes the re-stenting procedure to fail: a heightened immune response to the presence of the metal stent triggers the vessel to begin growing new cells, a process called neointimal hyperplasia. “The problem is the bare stent, not the way the stent is placed,” he says.
One way to overcome this problem might be the use of drug-eluting stents, which are experimental stents that are coated with drugs that block neointimal hyperplasia.
Radiation is used to prevent neointimal proliferation in the old stent, but it may prevent the normal growth of cells needed to secure the new stent to the blood vessel, suggests Morino.
Co-authors are Thosaphol Limpijankit, M.D.; Yasuhiro Honda, M.D.; Alexandra J. Lansky, M.D.; Ron Waksman, M.D., Heidi N. Bonneau, R.N., M.S.; and Gary S. Mintz, M.D.
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